JPH0545771B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an engine intake device, and in particular,
The present invention relates to an improvement in an engine intake system that improves output by utilizing inertia supercharging by synchronizing the air column vibration of the intake system with the intake period.

(Prior art) Generally, the flow in the intake pipe is a so-called pulsating flow.
When the intake valve opens and the intake stroke begins, the negative pressure generated within the cylinder accelerates the air column in the intake pipe and flows into the cylinder. During this time, the cylinder internal pressure and volume change with the downward movement of the piston, and at the same time, the intake pipe internal pressure and speed also gradually change both in time and location. The pressure waves generated in the cylinder propagate through the intake pipe, are reflected at the surge tank, and return to the cylinder, and this phenomenon is repeated in the intake system. By synchronizing the frequency of the pressure change caused by the downward movement of the piston with the natural frequency of the intake system, which is determined by the volume of the intake pipe and cylinder, an intake inertia effect can be obtained and the volumetric efficiency can be improved. It is well known that output can be achieved.

The natural frequency of the intake system is determined by the length and cross-sectional area of the intake passage, and the average cylinder volume during the intake period.The range of engine speeds that are synchronized with this natural frequency is widened, and the output is achieved by utilizing the intake inertia effect. In order to expand the improvement range, various techniques have been proposed in which the length or area of the intake passage is variable (for example, Japanese Patent Application Laid-Open Nos. 48-58214 and 115819-1989).
No., Japanese Patent Publication No. 58-119919).

However, these prior art techniques have problems such as the effect of expanding the range of output improvement by utilizing the intake inertia effect is small and insufficient, and widening the range of change requires a complicated mechanism. It is hoped that the structure will provide greater tuning over a wider range.

That is, for example, in a mechanism in which the length of the intake passage is changed over two or more stages to expand the tuning range, each passage length has a peak of the intake inertia effect, and if this is exceeded, This causes a large decrease in output and a drop in torque at the time of switching. In particular, when switching the passage length, making the intake passage for the low rotation range as long as possible and increasing the difference in length before and after switching will have a higher effect on improving output in the low rotation range.
This is preferable because the tuning range is wide. However, the greater the difference in length before and after switching, the greater the drop in torque at the time of switching, which may adversely affect drivability.

(Object of the Invention) In view of the above circumstances, the present invention expands the tuning range of the intake inertia effect by switching the intake passage shape, and improves the drop in torque that occurs in the switching region of the intake passage shape, It is an object of the present invention to provide an engine intake device that is capable of improving output over a wide range.

(Structure of the Invention) The intake device of the present invention is provided with a passage shape switching means for switching the shape of the intake passage according to the engine speed, and also includes a valve timing changing means for changing at least the closing timing of the intake valve. The valve timing of the intake valve is changed in the switching region of the intake passage shape so that the closing timing of the intake valve is earlier on the high rotation side than on the low rotation side within the switching region.

(Effects of the Invention) According to the present invention, in addition to expanding the tuning range of the intake inertia effect by switching the shape of the intake passage, the valve timing of the intake valve is changed from the low rotation side to the high rotation side in the switching region. By changing the valve closing timing to be earlier to improve the output at the time of switching and to improve the drop in torque, it is possible to effectively improve the output over a wide range.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional front view of a main part of a multi-cylinder engine equipped with an intake system, and FIG. 2 is a sectional view taken along the line - in FIG.

An intake port 3 and an exhaust port 4 are opened in the combustion chamber 2 of each cylinder of the engine 1.
An intake valve 5 and an exhaust valve 6 are disposed at the opening to the combustion chamber 2 . The intake passage 7 communicating with the intake port 3 has a surge tank 9 downstream of the throttle valve 8, is branched downstream of the surge tank 9, and is connected to each cylinder independently, and is provided with a fuel injection nozzle 10. ing.

The surge tank 9 is formed by a casing 11 and a cylindrical member 12 installed therein, and a passage shape switching means 13 for switching the passage length of the intake passage 7 is configured in the surge tank 9. ing. This casing 11 forms an intake manifold fastened to the cylinder head 15 of the engine 1, and extended portions of the intake passages 7 connected to each cylinder are formed along the circumferential direction of the casing 11, corresponding to each cylinder. Further, the internal space of the cylindrical member 12 constitutes an expansion chamber downstream of the throttle valve 8, in other words, a substantial surge tank serving as an intake air holding space, and an opening 12a is provided at the center of one end surface. The opening 12a communicates with the upstream intake passage 7 provided with the throttle valve 8 and serves as an intake inlet, and the cylindrical outer circumferential surface of the cylindrical member 12 partitions the internal space and an extension portion 7a of the intake passage 7 at the outer circumference. At the same time, each intake passage is made independent for each cylinder by being in contact with the inner wall surface of the extension portion 7a of the casing 11 for the adjacent cylinders. A communication port 12b on the outlet side communicating with the intake passage 7 of each cylinder is provided on the circumferential surface of the cylindrical member 12, and a switching valve 14 is disposed at the edge of the communication port 12b. The switching valve 14 is
This is for switching the communication path between the communication port 12b of the cylindrical member 12 and the intake passage 7 downstream of the surge tank 9 to be lengthened by communicating through the extension portion 7a or to be shortened by direct communication. The length of the independent intake passage 7 from the surge tank 9 to each cylinder can be changed by changing the length of the independent intake passage 7 from the surge tank 9 to each cylinder.

The switching valve 14 has its rotating shaft 14a linked to an actuator 16.
is configured to be driven and controlled by a control signal from a control means 21 (control unit) to change the length of the intake passage.

The cylinder head 15 of the engine 1 is provided with an intake side valve mechanism 22 for controlling the opening and closing of the intake valve 5 and an exhaust side valve mechanism 24 for controlling the opening and closing of the exhaust valve 6. This intake side valve operating mechanism 22 is provided with a valve timing changing means 23 that variably controls the valve timing of the intake valve 5.

The intake side valve operating mechanism 22 has an intake side camshaft 25 that is rotationally driven by a crankshaft (not shown) of the engine 1, and the rotation of the camshaft 25 opens and closes the intake valve 5 via a tappet 26. be done. The tappet 26 is fitted into and held by a rotating member 27 so as to be slidable in the vertical direction, and the rotating member 27 has a lower surface formed in an arc shape.
It is rotatably supported by the camshaft 25 so as to allow mutual rotation, and is provided so as to be rotatable around the camshaft 25. An actuator 29 for swinging the rotating member 27 around the rotation axis of the camshaft 25 via a rod 28 according to the operating state of the engine is attached to constitute the valve timing changing means 23. Actuator 29 of the valve timing changing means 23
It is also driven and controlled by a control signal from the control means 21 (control unit).

When the rod 28 is driven to move rightward in the figure by the operation of the actuator 29, the rotating member 27 is rotated in the same direction as the rotational direction (clockwise rotation) of the camshaft 25. When the rotating member 27 is rotated, the tappet 26 is also rotated by the rotating member 2.
7, the contact position between the cam surface and the upper surface of the tappet 26 relative to a specific angular position of the camshaft 25 changes to the lag side with respect to the rotational direction of the camshaft 25, and the valve timing of the intake valve 5 deviates to the lag side. It is. In this valve timing changing means 23, as shown in FIG. 3, the opening timing of the intake valve 5 is delayed as well as the closing timing as shown by the chain line when the rotation is high compared to when the rotation is low as shown by the solid line. However, if other valve timing changing means are used, the opening timing of the intake valve 5 remains the same and only the closing timing is changed to the delayed side, as shown by the broken line in Fig. 3. You can also do this.

An engine rotational speed signal from a rotational speed sensor 31 and a load signal from a load sensor 32 are inputted to the control means 21, and the control means 21 controls the passage shape switching means according to the engine rotational speed at least when the load is high. The length of the intake passage by 13 is switched so that the intake inertia effect is maximized, and the valve timing changing means 2
3, the closing timing of the intake valve 5 is changed to improve the output.

In FIG. 1, 33 is a cylinder block, and 34 is a piston.

Controlling the length of the intake passage by opening and closing the switching valve 14 according to the engine speed by the control means 21;
The control characteristics of the closing timing of the intake valve 5 will be explained with reference to FIGS. 4 and 5.

First, intake passage length control basically increases the passage length when the engine speed is low, and shortens the passage length when the engine speed rises to a high speed. As shown in Figure 4, the full-open torque characteristics with respect to changes in engine speed are curve A when air is supplied through a long intake passage, and curve B when air is supplied through a short intake passage, each with a peak at the time of inertia tuning. The torque decreases at rotational speeds before and after that, and the passage shape switching means 13 is operated with the point where both curves A and B intersect as a switching region.
Since the shock is large if this switching operation is performed suddenly, the switching valve 14 was operated on the side of the parallel line in Fig. 1 so that intake air was supplied only through the long passage in the low rotation range. Engine speed is the first
When the set rotational speed N1 is exceeded, the switching operation is gradually performed as the rotational speed rises, and at the second set rotational speed N2, the switching valve 14 rotates toward the solid line side in Fig. 1 to intake air only through a short passage. The range between the set rotational speeds N1 and N2 is a switching region in which the passage length is switched.

On the other hand, the control of the closing timing of the intake valve 5 is controlled by the fifth valve.
As shown in the figure, basically, in order to prevent intake air blowback and improve charging efficiency, the rise in combustion chamber pressure is delayed relative to the increase in engine speed, so the increase in engine speed This also delays the valve closing timing, and the valve closing timing is relatively later when the intake passage is long than when it is short. The valve closing timing requirement in the switching region is such that when the passage is long on the low rotation side, the valve closing timing is delayed in response to the increase in rotation, even after the inertia peak, at a timing that adapts to the characteristics of this long passage, and the switching is made. When the valve 14 opens and the effect of the short passage begins to appear, the valve closing timing is gradually advanced and made earlier, and as the short passage becomes predominant, the valve closing timing is further advanced so as to adapt to the characteristics of the short passage, and the switching region When the speed reaches the high speed side, the speed is controlled to be delayed in response to the increase in speed.

By controlling the intake valve 5 to close earlier in the intake passage length switching region as described above, it is possible to prevent a significant drop in torque in this switching region. In other words, in Fig. 4, when the intake valve closing timing is constant and the torque characteristics shown by solid lines A and B are shown, when the intake passage is long, the inertia peak is exceeded and the engine speed increases. If the valve closing timing is delayed, the torque can be increased as shown by the chain line, whereas if the valve closing timing is advanced in response to the decrease in engine speed until the inertia peak is reached when the intake passage is short. The torque can be increased as shown by the broken line, and by changing the valve closing timing according to each state in both switching regions, it is possible to improve the drop corresponding to the torque increase.

In contrast to the means for changing the closing timing of the intake valve as in the above embodiment, two intake ports are opened in the combustion chamber of the engine, and the valve timing of the intake valve that opens and closes one intake port is fixed, and the valve timing of the intake valve that opens and closes the other intake port is fixed. By making the valve timing of the intake valve that opens and closes the port variable using the same changing means as in the previous example, the opening period of the intake valve as a whole may be made variable. In this way, in the case where the valve opening period can also be changed (including the one shown by the broken line in FIG. 3), the tuning range of the intake inertia effect can be expanded as the valve opening period changes.

Furthermore, in the above embodiment, the passage shape switching means 13 for changing the length of the intake passage is constituted by the intake passage extension formed around the surge tank 9 and the switching valve 8 for switching the extension, so that the overall structure can be improved. It can be formed compactly, simplifying the structure, and ensuring reliable operation.

On the other hand, as a means for changing and driving the shape of the intake passage and the opening/closing timing of the intake valve, in addition to using the control means by the control unit as described above, an actuator that operates in response to exhaust pressure or the like can be employed as appropriate.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional front view of main parts of an engine having an intake system according to an embodiment of the present invention, and FIG.
3 is a valve opening curve diagram showing variations in the opening/closing timing of the intake valve due to the valve timing changing means; FIG. 4 is a characteristic diagram showing the relationship between engine speed and full opening torque; FIG. 5 is a characteristic diagram showing changes in the closing timing of the intake valve. 1...Engine, 3...Intake port, 5...Intake valve, 7...Intake passage, 9...Surge tank, 1
3...Passage shape switching means, 14...Switching valve, 21
. . . control means, 23 . . . valve timing changing means.

Claims (1)

[Claims] 1. A passage shape switching means is provided to change the shape of the intake passage leading to the cylinder, and the shape of the intake passage is changed to the air column in response to an increase in the engine rotation speed in order to synchronize the engine rotation speed and the air column vibration frequency and obtain an intake inertia effect. In an engine intake system in which the operation of the passage shape switching means is controlled to increase the vibration frequency,
Valve timing changing means for changing at least the closing timing of the intake valve is provided, and the intake valve is closed at least on the high rotation side from the low rotation side within the switching area, at least in the switching region of the intake passage shape by the passage shape switching means. An intake system for an engine, comprising a control means for operating the valve timing changing means so that the timing is earlier.